1. Field of the Invention
The present invention relates to mixing apparatus for mixing dissimilar liquids or mixing particulate matter with liquids. More particularly, the present invention relates to vertical mixers having a vertical shaft extending in a tank. Additionally, the present invention relates to mixing systems in which Venturis are utilized.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Batch liquid mixing has three important industrial applications. These applications include blending of multiple miscible liquids, suspending solids in a carrier liquid, and for promoting heat transfer. The volume of batch liquid is mixed by an internally-mounted mixing device, generally known as an agitator impeller. The impeller is a single propeller or turbine blade connected to a rotating shaft that is driven by an electric motor at a fixed rotational speed. In some applications, a variable-speed gearbox is installed to control the shaft rotational speeds.
There are two classes of impeller agitators, namely, axial-flow and radial-flow. Axial-flow impellers impart a current parallel with the axis of the impeller shaft. Radial-flow impellers generate currents in a tangential or radial direction to the axis of the impeller shaft. In these two classes of impellers, there exists three primary designs, namely, propeller, turbine and paddle. Each of these primary designs has a geometrical design variation. These three primary types of impellers are utilized in approximately 95% of batch liquid agitation systems.
Standard propellers have two, three or four blades, depending on the mixing application intensity. A revolving impeller traces out a helix in the liquid. A full revolution moves the liquid a fixed distance. The ratio of distance to the propeller diameter is known as the “pitch”. Propellers are member of the axial-flow class of impeller agitators. Turbines have six to eight blades mounted at the end of the agitator shaft. These are a member of the radial-class of impeller agitators. The turbine diameter is approximately 30 to 50% of the vessel diameter. Paddles are generally two or four blades mounted on the end of the agitator shaft. They are a subset of the radial class of impeller agitators. Typically, the paddle diameter is 50 to 80% of the tank diameter.
Blade and turbine propellers that are utilized in batch agitating and mixing have a generated induced flow that is unstable. As such, the circumferential flow velocity will fluctuate as the liquid leaves the tips of the blades. The agitator impeller is essentially a pumping device operating without the confines of a casing or direct inlet and outlet flow. As the impeller rotates, fluid is forced outwardly from the blade tip. The movement force is a vector that can be described by radial and tangential velocity components.
Unfortunately, in these prior art designs, there can be an improper mixing of the liquids or an ineffective mixing of the liquids. In those circumstances where particulate matter is to be mixed with a liquid, these types of prior mixing apparatus will have a tendency to cause the solids to drift toward the corners or edges of the tanks. As such, a clean-out, or other operation, may be necessary to reinstill these remaining solid particles within the liquid. These prior systems are generally ineffective in assuring that virtually all of the solid particulate material will be entrained or mixed with the liquid. These prior mixing apparatus are also less-than-effective in drawing the particulate matter from the bottom of the tank upwardly so as to be mixed with the liquid. Most of the solid particulate matter will have to be mixed as the solid particulate matter is drifting downwardly in the liquid from a supply introduced above the liquid.
In the past, various patterns of issued relating to mixing apparatus. For example, U.S. Pat. No. 5,152,606, issued on Oct. 6, 1992 to Borraccia et al., describes a mixer impeller shaft attachment apparatus which is adapted to mix and blend liquids and liquid suspensions in industrial and commercial applications. The mixer impeller is secured to the shaft by collars which are threaded on the ends of hubs from which the blades of the impeller extend. In order to secure the attachment of the collars to the hub, a locking key is inserted between the collar and the shaft. The inner periphery of the collars are tapered outwardly away from the shaft. The impeller is restrained against axial movement by the collar and against rotational movement by being keyed to the shaft and restricted by the ramp on the collar.
U.S. Pat. No. 5,158,434, issued Oct. 27, 1992 to R. J. Wettman, teaches a mixing impeller and impeller system for mixing and blending liquids and liquid suspensions. The impellers have a plurality of separate blades and have camber and twist. The angle at the tip of two diametrically disposed blades of a four blade impeller may have different blade angles at the tip than the other pair of blades. The impellers may be of different diameters and disposed in close proximity so that they are in independent relationship. The impellers and impeller systems provide axial flow over a large range of viscosities of the liquid or liquid suspension.
U.S. Pat. No. 5,316,443, issued on May 31, 1994 to J. M. Smith, teaches a reversible mixing impeller that is designed for the chemical processing industry to provide a generally axial flow when rotated in a first direction of rotation to provide a generally radial flow when rotated in the opposite direction of rotation. The blades are formed of sheet material with an edge which leads in the first direction of rotation being defined by a portion of the blade which is folded and turned in a chordwise sense to a limited extent back upon itself. The folded back leading edge forms a rearwardly facing concavity which bases the blade trailing edge.
U.S. Pat. No. 5,813,837, issued on Sep. 29, 1998 to Yamamoto et al., describes an axial-flow impeller for mixing liquids. This axial-flow impeller has a maximum blade with less than 20% of the impeller diameter. The pitch angle at the radial position is 12° to 22°. The width at the tip and portion of the blade is 12 to 75% of the width at the radial position.
U.S. Pat. No. 6,334,705, issued on Jan. 1, 2002 to R. J. Weetman, discloses a fluid mixing impeller with a shear generating Venturi. This impeller is used in a sparging system for dispersion and for mass transfer of a liquid phase or a gaseous phase into a liquid which is being mixed or agitated. The impeller forms a shear field which breaks the phase being dispersed in defined bubbles which are dispersed by the impeller. A structure is provided which forms a Venturi that is located on the side or sides of the blade where the phase occurs, in particular, in the high-velocity region near the tip of the blade. The structure is provided by a pair of proplets in the vicinity of the tip end of the blade which form a wedge-shaped flow path there between.
It is an object of the present invention to provide a mixing apparatus that enhances the mixing of dissimilar fluids and/or the mixing of fluids with solids.
It is another object of the present invention to provide a mixing apparatus that reduces the static head in the front of the mixing element.
It is another object of the present invention to provide a mixing apparatus that reduces the horsepower requirements for the mixer.
It is still another object of the present invention to provide a mixing apparatus that lifts solids from the bottom and/or corners of the tank.
It is a further object of the present invention provide a mixing apparatus that provides increased turbulence during the mixing process.
It is another object of the present invention provide a mixing apparatus that dynamically shears particles.
It is a further object of the present invention provide a mixing apparatus that generates overlapping vortices.
It is another object of the present invention to provide a mixing apparatus that can be utilized with various tank configurations.
It is another object of the present invention to provide a mixing apparatus that allows for the control of boundary layers of fluids.
It is still a further object of the present invention to provide a mixing apparatus that enhances the physical properties of the liquid constituents.
It is still further object of the present invention to provide a mixing apparatus that effectively mixes liquids and slurries without degrading the product.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.